Trump got vitamin D infusions in the hospital.
It's also something that taking a daily pill for will not have immediate effects. If you take OTC supplements today you won't see your levels increase for days or weeks.
Whether or not such a bump gives the same benefits as slow ramping (and if it delivers then more quickly or not) is something I haven’t found any studies on - but I have found in the past studies indicating sun exposure is better than supplements for the same attained blood vitamin D levels (not surprising, as vitamin D is far from the only result of sun exposure)
That said, I can totally imagine people downing a megadose of vitamin D, declaring themselves immune, and going out to lick doorknobs immediately.